BIOLOGY

There are different types of vaccine.There has been lots of debates about relative merits of live and killed vaccine.Live vaccines are much more effective though they were more risky in the past.Other factor like safety, costs, politcs and social acceptance can determines whether there is high or more more uptake of a particular vaccine and whether it's successful.
There are many purpose for using and making vaccines.For example in UK three vaccines have licensed for the typhoid vaccination

The above second was the recently introduced in 1992.It needs leat number of doses and is most preferred.The safety of vaccine is one of the most important issued in the developed countries but for the developing countries the cost of vaccines and the way of delivering of it is most important.

In recent days the development and the productions of the vaccines are using techniques of genetic engineering.Different pathogens could not be cultured outsides their natural hosts.Therefore, the conventional approach to vaccinations could not be used.For e.g. bacterium causing leprosy or mycobacterium leprae and microbe causing human syphills or treponema pallidum have never grown outside of the body(victro).Therefore it's diffucult to generate inactivated vaccines or live attenuated with the help of culturing techniques.In this example the recombinate DNA technology offer alternative approaches, which allows genes antigens for transferring from this organisms to much more useful host like as E-coil, yeasts or mammalian cells, which is used to produce huge quantity of antigenes for vaccine.For e.g. it is easy to identify express and clone the surgace antigen gene of hepatitis.But all the protective antigens are difficult t develop.